(i) Field of the Invention
The present invention relates to a photoelectric back plane board comprising an optical data bus including a long plate of a light transmissive material having one side formed into a stepwise configuration and signal light incoming/outgoing areas formed by sloping each end surface of each step approximately at 45 degrees in relation to the plate surface, and relates to an information processing system using the photoelectric back plane board.
(ii) Description of the Related Art
To improve the processing performance of a signal processing unit, which employs a parallel architecture comprising a back plane board (mother board) and a plurality of nodes (daughter board), enhancement of the bandwidth by increasing the speed of transmission through a bus and bit multiplication has been sought.
Although further speed increase is required for such a signal processing unit employing a parallel architecture, the achievement of further speed increases using a conventional electrical wiring requires a circuit board design for reducing noises and delay with respect to the mother board and the daughter board. Optical fiber interconnection also has been introduced for increasing speed, even though it leads to further complicated wiring.
While increasing speed of a signal processing unit by the conventional electrical wiring is sought, increasing speed of a signal processing unit by intra-system optical interconnection technology called optical interconnection has been considered. As the outline of optical interconnection technology is described, for example, in The Transactions of the Institute of Electronics, Information and Communication Engineers, Vol.79 (No.9), September, 1996, xe2x80x9cOptical Interconnection Technology and its Applicationsxe2x80x9d by Osamu WADA, pp.907-909 and in Journal of Japan Institute of Electronics Packaging, Vol. 1, No.3 (1998), xe2x80x9cToward New Computing Systems with Optical Interconnectionxe2x80x9d by Masatoshi ISHIKAWA, pp.176-179, various forms may be proposed depending on the configuration of a system.
However, when optical interconnection utilizing optical fibers as a signal transmission medium is introduced not only into systems for industrial use but also into systems commonly used in offices and homes, there are problems, such as high packaging cost due to need for accurate positioning of optical connections and difficulty in realizing interconnection of multiple nodes with a simple structure.
As technology to solve these problems, an optical data bus 80 as shown in FIGS. 8A-8C was proposed at The 25th Symposium on Optics, 2000, Lecture No. 8, xe2x80x9cStudy on Backplane Optics and Apply to Optical Data Busxe2x80x9d by Junji OKADA et al.
The optical data bus 80, which comprises a long plate of light transmissive material (for example, a light transmissive resin composed of an acrylic having a refractive index of 1.49 and an olefin polymer having a refractive index of 1.525, or the like), is a translucent transmission medium for transmitting signal light in the longitudinal direction by repetitive internal reflection.
Specifically, the optical data bus 80 comprises, as shown in FIGS. 8A and 8B, an approximately rectangular substrate of light transmissive resin having one longitudinal side thereof formed into a step-wise configuration, the steps being dimensioned such that light emitting elements (e.g. laser diodes LD) or light receiving elements (e.g. photo diodes PD) can be arranged from the side of one longitudinal end toward the other end. Signal light incoming/outgoing areas 82 are formed by sloping each longitudinal end of each of the steps at 45 degrees in relation to the surface of the substrate. FIG. 8A is a plan view of the optical data bus 80 and FIG. 8B is a side view thereof.
To perform optical transmission using the optical data bus 80, a reflective diffusion portion (e.g. light diffusive film) 84 is provided on the end surface opposite to the signal light incoming/outgoing areas 82 of the optical data bus 80 so that the optical data bus 80 has the diffusion angle in the thickness direction of 0.2 degrees and the diffusion angle in the width direction of 40 degrees. In addition, a laser diode LD or a photo diode PD is disposed above each of the signal light incoming/outgoing areas 82 such that each optical axis intersects perpendicularly to the substrate surface of the optical data bus 80.
Once the laser diode LD disposed above a given signal light incoming/outgoing area is activated and laser beam is irradiated from above the optical data bus 80, the entering light is totally reflected from the end surface sloped at 45 degrees in relation to the substrate surface of the optical data bus 80 and transmitted toward the reflective diffusion portion 84, then reflected and diffused from the reflective diffusion portion 84. The reflected light, in turn, is totally reflected from the end surface of each signal light incoming/outgoing area 82 and emitted from the top surface of the optical data bus 80. Thus, the optical signal emitted from the laser diode LD is transmitted to the photo diode PD disposed above the signal light incoming/outgoing area 82, with the result that the signal transmitted through the laser diode LD and the optical data bus 80 can be obtained from the current flowing through the photo diode PD.
Therefore, if a back plane board including the above described optical data bus as a signal transmission medium is put into practical use, it is possible to achieve interconnection, with a simple configuration, of a plurality of circuit boards provided with at least one of light emitting means comprising an electronic circuit for generating an electrical signal and a light emitting element for converting the electrical signal to an optical signal, and light receiving means comprising a light receiving element for converting an optical signal to an electrical signal and an electronic circuit for processing the converted electrical signal.
The use of the above described optical data bus as a signal transmission medium, however, presents problems of how to fix the optical data bus. Specifically, it is required to relatively position the optical data bus, the light emitting element and the light receiving element such that light is totally reflected from the signal light incoming/outgoing areas and an optical signal is transmitted by repetitive internal reflection through the optical data bus, which is a translucent transmission medium. Also, since optical transmission in the optical data bus utilizes the air having a refractive index of 1 as a cladding layer, it is preferable not to use an adhesive for fixing the optical data bus. However, there has not been provided any appropriate fixing means in order to use, as a signal transmission medium, an optical data bus having a step-wise configuration, as shown in FIGS. 8A to 8C. Therefore, there has been a demand for an optical data bus fixing device which enables efficient transmission of an optical signal using an optical data bus as above.
The inventors of the present invention have devised a method for fixing such an optical data bus by means of a fixing board comprising a flat plate provided with a recess for insertion of an optical data bus opened corresponding to the contour of the optical data bus and a positioning portion for positioning a light emitting element or a light receiving element above each signal light incoming/outgoing area of the optical data bus inserted into the recess for insertion of an optical data bus.
More specifically, the optical data bus is inserted into the recess for insertion of an optical data bus formed in the fixing board and is held with a certain holding member, and then the light emitting element and the light receiving element are positioningly fixed above respective signal light incoming/outgoing areas of the optical data bus inserted into the recess for insertion of an optical data bus by using the positioning portion formed in the fixing board.
The use of such a fixing board facilitates significantly simple setting of the relative positions of the signal light incoming/outgoing areas of the optical data bus and the light emitting element and the light receiving element as well as fixation of the optical data bus without using an additive. Thus, it is possible to meet the above described demand.
However, to actually perform optical communication using an optical data bus fixed within the fixing board, it is necessary to connect the light emitting element and the light receiving element relatively positioned on the optical data bus with a plurality of circuit boards (the above-mentioned daughter boards), so that activation of the light emitting element and processing of the received light may be performed by respective circuit boards.
This has posed other issues of how to connect the light emitting element and the light receiving element, which have been relatively positioned with respect to the optical data bus by using the above described fixing board, with the respective circuit boards which actually perform optical communication by means of the light emitting element and the light receiving element, and of how to control the signal processing performed by the respective circuit boards.
Specifically, optical communication between a plurality of circuit boards by means of the light emitting element and the light receiving element, which have been relatively positioned with respect to the optical data bus by the above described fixing board, requires adjustments, such as synchronizing the activation of the light emitting elements and the processing of the received light performed in the respective circuit boards. Accordingly, it is necessary to provide a variety of control signals, such as a synchronizing signal, to the respective circuit boards. The above-mentioned issue is, in other words, how to connect the light emitting elements and the light receiving elements positioningly fixed to the fixing board with the respective circuit boards in order to facilitate providing signals to the respective circuit boards.
Furthermore, power supply is necessary for the respective circuit boards. In the case where exclusive power lines are employed for power supply, the wiring operation of those exclusive power lines is troublesome. An alternative way is to provide the fixing board with the function of supplying power to the respective circuit boards, so that power may be supplied from the fixing board to the respective circuit boards once the respective circuit boards are mounted on the fixing board. Power supply in such a manner also leads to the issue of how to connect the fixing board with the respective circuit boards.
An object of the present invention, which is to solve the above issues, is to provide a photoelectric back plane board, wherein the optical data bus having a step-wise configuration, and the light emitting elements and the light receiving elements are located at a given relative position, and wherein connection of the circuit board for optical communication with the light emitting elements and the light receiving elements, and signal input/output and power supply to/from the circuit board are facilitated, and to provide an information processing system using the photoelectric back plane board.
This and other objects are accomplished with a photoelectric back plane board according to the present invention. The photoelectric back plane board comprises a multiple optical data bus fixing board provided with a plurality of recesses for insertion of an optical data bus formed therein, and optical data buses are inserted and fixed in the recesses for insertion of an optical data bus, respectively. By mounting the photoelectric back plane board on a printed circuit board, the optical data buses are positioningly fixed on the printed circuit board. The printed circuit board, or both of the printed circuit board and the multiple optical data bus fixing board are provided with through holes for positioningly fixing a plurality of optical connectors holding a plurality of light emitting elements and light receiving elements for respectively inputting/outputting optical signals to/from signal light incoming/outgoing areas of the optical data buses.
The plurality of recesses for insertion of an optical bus are formed in the multiple optical data bus fixing board at approximately the same intervals, so that when the optical data buses are inserted into the respective recesses for insertion of an optical bus, the corresponding signal light incoming and outgoing areas of the respective optical data buses are aligned on substantially straight lines, respectively. This renders it possible for the light emitting elements and light receiving elements to be aligned on substantially straight lines along the surfaces of a circuit board for optical communication when the circuit board is mounted on the optical connector.
In other words, if only the corresponding signal light incoming/outgoing areas of the respective optical data buses are aligned on substantially straight lines, the optical connector can hold the plurality of light emitting elements and light receiving elements for respectively inputting/outputting signal light to/from the signal light incoming/outgoing areas of the respective optical data buses aligned in rows and the circuit board arranged along the direction of the rows.
In the photoelectric back plane board according to a first embodiment of the invention, an optical connector, i.e. a circuit board, is assigned to one or more groups of signal light incoming/outgoing areas, each group consisting of signal light incoming/outgoing areas of the respective optical data buses aligned on a substantially straight line on the printed circuit board, and the respective optical connectors and the circuit boards mounted on the respective optical connectors are arranged on the printed circuit board so as to cross over, or traverse the respective optical data buses.
In the case where recesses for insertion of an optical data bus are formed as described above, an optical connector and a circuit board are disposed per one or a certain number of adjacent signal light incoming/outgoing areas arranged in the longitudinal direction of an optical data bus. Therefore, a plurality of optical connectors holding light emitting elements and light receiving elements may be all common. Particularly, as described later in preferred embodiments, in which the recesses for insertion of an optical data bus are formed such that the respective signal light incoming/outgoing areas of all the optical data buses are arranged on an orthogonal grid, the optical connectors and the circuit board mounted thereon may be aligned along the outer shape of the multiple optical data bus fixing board.
The printed circuit board is provided thereon with a plurality of electrical connector for supplying power or inputting/outputting signals to/from the respective circuit boards arranged as above, and supplies power or inputting/outputting signals via the electrical connectors to/from the respective circuit boards.
According to the photoelectric back plane board of the first embodiment, by utilizing the through holes formed in the printed circuit board, or both of the printed circuit board and the multiple optical data bus fixing board, not only the relative positioning of the optical data buses and the light emitting elements and light receiving elements held in the optical connectors is easily achieved, but also supplying power and inputting/outputting signals from the printed circuit board to the circuit board mounted on the optical connector via the electrical connector can be performed.
Thus, the photoelectric back plane board according to the first embodiment facilitates development of an information processing system by which high-speed data communication among a plurality of circuit boards (above-mentioned daughter boards) using optical data buses is enabled.
Furthermore, the multiple optical data bus fixing board in the photoelectric back plane board according to the first embodiment is removably mounted on the printed circuit board as a base, and therefore the optical data bus can be replaced without directly touching the same by replacing the multiple optical data bus fixing board with the optical data bus fixed therewithin. This can prevents the optical data bus from getting dirty or damaged while replacing the same, and leads to improvement in efficiency of maintenance work.
In a photoelectric back plane board according to another embodiment of the invention, an optical data bus guide plate is employed instead of the multiple optical data bus fixing board according to the first embodiment.
The optical data bus guide plate includes a plate having approximately the same thickness as the optical data bus, and is provided with a plurality of through guide holes having a contour corresponding to the configuration of the optical data bus. The guide holes are formed at approximately the same intervals so that when the respective optical data buses are inserted into the guide holes, the corresponding signal light incoming and outgoing areas of the respective optical data buses may be aligned on substantially straight lines, respectively.
Once the optical data bus guide plate is mounted on the printed circuit board, the optical data buses are inserted and fixed in recesses for insertion of an optical data bus formed with the guide holes and the surface of the printed circuit board by mounting the optical data bus guide plate on the printed circuit board.
The printed circuit board, or both of the printed circuit board and the multiple optical data bus fixing board are provided with through holes for positioningly fixing a plurality of optical connectors which hold a plurality of light emitting elements and light receiving elements for respectively inputting/outputting optical signals to/from signal light incoming/outgoing areas of the optical data bus. The optical connector is adopted to have a circuit board for optical communication mounted thereon in the same manner as in the optical connector of the first embodiment.
The printed circuit board, on which a plurality of electrical connectors are fixed for supplying power or inputting/outputting signals to circuit boards mounted on the optical connectors positioned on the printed circuit board via the through holes, as in the first embodiment, supplies power or input/output signals to/from the respective circuit boards via the respective electrical connectors.
According to a further embodiment of the photoelectric back plane board, a plurality of single data bus fixing board each having a single recess for insertion of an optical data bus is employed instead of the multiple optical data bus fixing board in the first embodiment.
The plurality of single optical data bus fixing boards are removablly mounted on the printed circuit board such that when the respective optical data buses are inserted and fixed in the recesses for insertion of an optical data bus, the corresponding signal light incoming/outgoing areas of the respective optical data buses are aligned on substantially straight lines, respectively.
The printed circuit board is provided with through holes formed therein, for positioningly fixing a plurality of optical connectors on the printed circuit board, as in the other embodiments. Also, a plurality of electrical connectors for supplying power or inputting/outputting signals to/from circuit boards mounted on the optical connectors which are positioned via the through holes are fixed on the surface of the printed circuit board, on which the single optical data bus fixing board is stacked in layers. The printed circuit board supplies power or inputting/outputting signals to/from the respective circuit boards via the electrical connectors.
According to yet another embodiment of the photoelectric back plane board, instead of using a member for fixing an optical data bus, such as a multiple or single data bus fixing board, or an optical data bus guide plate, a printed circuit board having a plurality of recesses for insertion of an optical data bus formed directly in the surface thereof so that a plurality of optical data buses can be fixed directly on the printed circuit board.
In the printed circuit board, the plurality of recesses for insertion of an optical data bus are formed at approximately the same intervals so that when the respective optical data buses are inserted into the recesses for insertion of an optical data bus, the corresponding signal light incoming/outgoing areas of the respective optical data buses may be aligned on substantially straight lines, respectively.
As in the other embodiments, the printed circuit board is provided with through holes formed therein for positioningly fixing a plurality of optical connectors on the printed circuit board, and a plurality of electrical connectors for supplying power or inputting/outputting signals to/from the respective circuit boards mounted on the optical connectors which are positioned via the through holes. Thus, the printed circuit board may supply power or inputting/outputting signals to/from the respective circuit boards via the electrical connectors.
In a photoelectric back plane board according to a further embodiment of the present invention, the optical data bus fixing board is fixed on the printed circuit board by being positioned by means of at least one positioning member with respect to the printed circuit board at one or a plurality of points on a straight line substantially perpendicular to the longitudinal direction of the optical data bus, and by being pressed on the printed circuit board by a guide rail for covering the optical data bus fixing board from above at a position distant from the point at which the optical data bus fixing board is positioned with respect to the printed circuit board.
In the photoelectric back plane board of the present embodiment, the joints of the optical data bus fixing board and the printed circuit board are limited to the positioning points by the positioning members, i.e. at one or a plurality of points on a straight line substantially perpendicular to the longitudinal direction of the optical data bus, so that the optical data bus fixing board may expand or contract on the printed circuit board with a focus on the joints when the ambient temperature changes.
As a result, it is possible to prevent the optical data bus fixing board from being deformed or cracked due to the change of the ambient temperature, thereby to prevent deterioration of the communication performance by means of the photoelectric back plane board.